NAME
"Config::XPath" - retrieve configuration data from XML files by using
XPath
SYNOPSIS
use Config::XPath;
my $conf = Config::XPath->new( filename => 'addressbook.xml' );
## Basic data retrieval
my $bob_phone = $conf->get_string( '//user[@name="bob"]/@phone' );
my %jim_details = $conf->get_attrs( '//user[@name="jim"]' );
my @everyone_with_fax = $conf->get_list( '//user[@fax]' );
print " $_ has a fax\n" for @everyone_with_fax;
my $phone_map = $conf->get_map( '//user', '@name', '@phone' );
print " $_ has a phone: $phone_map->{$_}\n" for sort keys %$phone_map;
## Subconfigurations
my $james_config = $conf->get_sub( '//user[@name="james"]' );
my $james_phone = $james_config->get_string( '@phone' );
foreach my $user_config ( $conf->get_sub_list( '//user[@email]' ) ) {
my $town = $user_config->get_string( 'address/town' );
print "Someone in $town has an email account\n";
}
DESCRIPTION
This module provides easy access to configuration data stored in an XML
file. Configuration is retrieved using XPath keys; various methods exist
to convert the result to a variety of convenient forms.
If the methods are called as static functions (as opposed to as object
methods) then they access data stored in the default configuration file
(details given below).
Subconfigurations
By default, the XPath context is at the root node of the XML document.
If some other context is required, then a subconfiguration object can be
used. This is a child "Config::XPath" object, built from an XPath query
on the parent. Whatever node the query matches becomes the context for
the new object. The methods "get_sub()" and "get_sub_list()" perform
this task; the former returning a single child, and the latter returning
a list of all matches.
CONSTRUCTOR
$conf = Config::XPath->new( %args )
This function returns a new instance of a "Config::XPath" object,
containing the configuration in the named XML file. If the given file
does not exist, or an error occured while reading it, an exception
"Config::XPath::Exception" is thrown.
The %args hash requires one the following keys to provide the XML
source:
filename => $file
The filename of the XML file to read
xml => $xml
A string containing XML data
ioref => IO
An IO handle reference
Also may be provided:
parser => $parser
An "XML::Parser" object
If a parser is not provided, one will be constructed internally.
METHODS
$result = $config->get( $paths, %args )
This method retrieves the result of one of more XPath expressions from
the XML file. Each expression should give either a text-valued element
with no sub-elements, an attribute, or an XPath function that returns a
string, integer or boolean value.
The $paths argument should contain a data tree of ARRAY and HASH
references, whose leaves will be the XPath expressions used. The $result
will be returned in a similar tree structure, with the leaves containing
the value each expression yielded against the XML config. The %args may
contain a "default" key, which should give default values for these
results, also in a similar tree structure.
If no suitable node was found matching an XPath expression and no
corresponding "default" value is found, then an exception of
"Config::XPath::ConfigNotFoundException" class is thrown. If more than
one node is returned, or the returned node is not either a plain-text
content containing no child nodes, or an attribute, then an exception of
class "Config::XPath::BadConfigException" class is thrown.
$paths A tree data structure containing ARRAY and HASH references, and
XPath expressions stored in plain scalars.
%args A hash that may contain extra options to control the operation.
Supports the following keys:
"default"
Contains a tree in the same structure as the $paths, whose
leaf values should be returned instead of the value yielded
by the XPath expression, in the case that no nodes match it.
$str = $config->get_string( $path, %args )
This function is a smaller version of the "get" method, which only works
on a single string path.
$path The XPath to the required configuration node
%args A hash that may contain extra options to control the operation.
Supports the following keys:
"default"
If no XML node is found matching the path, return this value
rather than throwing a
"Config::XPath::ConfigNotFoundException".
$attrs = $config->get_attrs( $path )
This method retrieves the attributes of a single element in the XML
file. The attributes are returned in a hash, along with the name of the
element itself, which is returned in a special key named '+'. This name
is not valid for an XML attribute, so this key will never clash with an
actual value from the XML file.
If no suitable node was found matching the XPath query, then an
exception of "Config::XPath::ConfigNotFoundException" class is thrown.
If more than one node matched, or the returned node is not an element,
then an exception of class "Config::XPath::BadConfigException" class is
thrown.
"*$path*"
The XPath to the required configuration node
@results = $config->get_list( $listpath; $valuepaths, %args )
This method obtains a list of nodes matching the $listpath expression.
For each node in the list, it obtains the result of the $valuepaths with
the XPath context at each node, and returns them all in a list. The
$valuepaths argument can be a single string expression, or an ARRAY or
HASH tree, as for the "get()" method.
If the $valuepaths argument is not supplied, the type of each node
determines the value that will be returned. Element nodes return a
hashref, identical to that which "get_attrs()" returns. Other nodes will
return their XPath string value.
$listpath
The XPath expression to generate the list of nodes.
$valuepaths
Optional. If present, the XPath expression or tree of
expressions to generate the results.
%args A hash that may contain extra options to control the operation.
Supports the following keys:
"default"
Contains a tree in the same structure as the $valuepaths,
whose leaf values should be returned instead of the value
yielded by the XPath expression, in the case that no nodes
match it.
$map = $config->get_map( $listpath, $keypath, $valuepaths, %args )
This method obtains a map, returned as a hash, containing one entry for
each node returned by the $listpath search, where the key and value are
given by the $keypath and $valuepaths within each node. It is not an
error for no nodes to match the $listpath.
The result of the $listpath query must be a nodeset. The result of the
$keypath is used as the hash key for each node, and must be convertable
to a string, by the same rules as the "get_string()" method. The value
for each node in the hash will be obtained using the $valuepaths, which
can be a plain string, or an ARRAY or HASH tree, as for the "get()"
method.
The keys obtained by the $keypath should be unique. In the case of
duplicates, the last value from the nodeset is used.
$listpath
The XPath to generate the nodeset
$keypath
The XPath within each node to generate the key
$valuepaths
The XPath expression or tree of expressions within each node to
generate the value.
%args A hash that may contain extra options to control the operation.
Supports the following keys:
"default"
Contains a tree in the same structure as the $valuepaths,
whose leaf values should be returned instead of the value
yielded by the XPath expression, in the case that no nodes
match it.
$subconfig = $config->get_sub( $path )
This method constructs a new "Config::XPath" object whose context is at
the single node selected by the XPath query. The newly constructed child
object is then returned.
If no suitable node was found matching the XPath query, then an
exception of "Config::XPath::ConfigNotFoundException" class is thrown.
If more than one node matched, then an exception of class
"Config::XPath::BadConfigException" is thrown.
$path The XPath to the required configuration node
@subconfigs = $config->get_sub_list( $path )
This method constructs a list of new "Config::XPath" objects whose
context is at each node selected by the XPath query. The array of newly
constructed objects is then returned. Unlike other methods, it is not an
error for no nodes to match.
$path The XPath for the required configuration
DEFAULT CONFIG FILE
In the case of calling as static functions, the default configuration is
accessed. When the module is loaded no default configuration exists, but
one can be loaded by calling the "read_default_config()" function. This
makes programs simpler to write in cases where only one configuration
file is used by the program.
read_default_config( $file )
This function reads the default configuration file, from the location
given. If the file is not found, or an error occurs while reading it,
then an exception of "Config::XPath::Exception" is thrown.
The default configuration is cached, so multiple calls to this function
will not result in multiple reads of the file; subsequent requests will
be silently ignored, even if a different filename is given.
$file The filename of the default configuration to load
FUNCTIONS
Each of the following functions is equivalent to a similar method called
on the default configuration, as loaded by "read_default_config()".
$str = get_config_string( $path, %args )
Equivalent to the "get_string()" method
$attrs = get_config_attrs( $path )
Equivalent to the "get_attrs()" method
@values = get_config_list( $path )
Equivalent to the "get_list()" method
$map = get_config_map( $listpath, $keypath, $valuepath )
Equivalent to the "get_map()" method
$map = get_sub_config( $path )
Equivalent to the "get_sub()" method
$map = get_sub_config_list( $path )
Equivalent to the "get_sub_list()" method
EXCEPTIONS
Config::XPath::Exception
This exception is used as a base class for config-related exceptions. It
is derived from "Error", and stores the config path involved.
$e = Config::XPath::Exception->new( $message; $path )
The path is optional, and will only be stored if defined. It can be
accessed using the "path" method.
$path = $e->path
Config::XPath::ConfigNotFoundException
This exception indicates that the requested configuration was not found.
It is derived from "Config::XPath::Exception" and is constructed and
accessed in the same way.
Config::XPath::BadConfigException
This exception indicates that configuration found at the requested path
was not of a type suitable for the request made. It is derived from
"Config::XPath::Exception" and is constructed and accessed in the same
way.
Config::XPath::NoDefaultConfigException
This exception indicates that no default configuration has yet been
loaded when one of the accessor functions is called directly. It is
derived from "Config::XPath::Exception".
$e = Config::XPath::NoDefaultConfigException->new( $path )
SEE ALSO
* XML::XPath - Perl XML module that implements XPath queries
* Error - Base module for exception-based error handling
AUTHOR
Paul Evans